Tag Archives: pXRF

Hi! This is Eve Mayberger with another update on the Ancient Panel Painting: Examination, Analysis, and Research (APPEAR) project (see earlier posts here and here). I recently investigated the pigments used on the three Fayum mummy portraits with the portable x-ray fluorescence (pXRF). While the pXRF results for all three portraits are interesting, I am going to briefly discuss the findings for the Portrait of a Woman (E16214).

One of the major advantages of pXRF is that it is a non-destructive technique that uses x-rays to identify specific elements. The technique can help to characterize pigments and metal alloy components. It is important to remember that pXRF is a surface technique and will only detect elements present on the surface. I decided to analyze the seven different colors used on the mummy portrait to determine if there are any elemental differences.

Collecting data with the Brucker pXRF

All the test locations recorded prominent peaks for calcium (Ca), iron (Fe), and lead (Pb). Although there is some variation in peak heights across the test spots, it is important to remember that pXRF is a qualitative not a quantitative technique. See below for a representative spectrum for six out of the seven analyzed locations.

The green used to paint the gemstones on the woman’s necklace has an additional peak for copper (Cu). This is not surprising as many greens have a copper component. In ancient Egypt, the greens were generally made with malachite or green earths, or from a mixture of blue and yellow pigments. While malachite is a copper-based compound, more analysis is needed to confidently identify the green pigment used for the gemstones.

It should be noted that not all pigments can be identified with pXRF alone. Some organic pigments, such as madder, cannot be detected with pXRF. In addition to using analytical instrumentation, it is also important to know what colorants are expected on specific artifacts to help limit the number of possible pigments.

Be sure to visit the blog in the upcoming weeks to read more about the APPEAR project!

Last week, I wrote about x-raying the fragments of a painted wooden coffin, as part of the conservation treatment. The radiographs helped us see what is under the painted surface. We then turned to the painted surface itself. Through cleaning, we revealed how beautiful and well-preserved the decoration is. I described the cleaning process (and linked to a short video showing the process!) in a previous post.

E12617A-C coffin fragments before (left) and after (right) cleaning

While it was impossible to see the full range of colors on the boards before cleaning, after cleaning we could see that there were several different colors used to decorate the surface, including two different yellows, red, green, black, and paint that appears black but where it is abraded/damaged looks blue. After much experience working on ancient Egyptian painted wooden artifacts, I knew enough to suspect that some of the paint that appears black is actually Egyptian blue.

It appears that there is a lot of black paint here, but not all of this paint was originally black. The yellow arrows point to black paint while the red arrows point to areas that were originally blue.

If you’ve been reading our blog, you are probably very familiar with one of our favorite photography techniques for Egyptian material, visible-induced infrared luminescence imaging. I have written about it previously, where I explain the process and the equipment we use (follow this link to the post).

Sure enough, it worked beautifully to confirm, and to allow us to see the Egyptian blue on this object:

All of the darkened/altered Egyptian blue shows up as bright white in the center image above, and the red areas in the false color image on the right help to further visualize where the blue is in relation to the rest of the painted design. Gotta love this technique!

So that’s great for determining the presence and location of Egyptian blue. But what about some of the other colors? I was particularly curious about the two different yellows and the green. In the case of the yellows, are they two different pigments? And as for the green, which pigment(s) were used to produce this color? Without (for the moment – more about that later) knowing the exact time period of this object, I knew there could be at least a couple different options, including Egyptian green (or green frit), and green earth.

To gather more information about these pigments, I carried out portable x-ray fluorescence analysis (pXRF) in select areas on the boards. I collected data from the following areas, marked with colored X’s in the image below:

pXRF analysis locations, with elements detected listed in order of relative peak height, from large to small

As you can see, I labeled the image with the findings from the pXRF analysis. It looks like the two different yellows are indeed two different pigments: the darker, more orange-yellow paint contains primarily calcium and iron, suggesting that this is an ochre, while the brighter yellow paint contains calcium, arsenic, and iron. The relatively large amount of arsenic suggests that this yellow was produced using orpiment (arsenic sulfide).

The green paint also contains arsenic, as well as calcium, copper, and iron. So it appears that the green was produced by mixing an arsenic-containing material (orpiment?) with a copper-containing pigment. Due to the lack of any visible-induced IR luminescence in the green areas, I don’t think that these areas could contain any Egyptian blue, so perhaps the green was made by mixing orpiment with Egyptian green. And as you can see, the blue paint does not contain any arsenic, but does contain calcium, copper, and iron, which we expect to find in areas painted with Egyptian blue. Further analysis will be necessary to determine exactly which pigments were used in the yellow and green areas, but we have discovered a lot using these completely non-invasive techniques!

In my next post about this object, I hope to write about the translation and interpretation, for which I’ll need to consult with the museum’s Egyptologists. In the meantime, if you’d like to learn more about green pigments on ancient Egyptian objects, and more applications of multispectral imaging on Egyptian objects, check out this really great video presentation by Kelsey Museum Conservator Carrie Roberts (originally presented at the 2014 ASOR Annual Meeting):

I think it’s about time we introduce you to a special occupant of the Artifact Lab.

This baby boy mummy, who dates to the Third Intermediate Period (1075-656 BCE), has been in our collection since 1898, when he was donated to the museum by Dr. Henry Shurtleff.

Photograph of the baby boy mummy ca. 1930

In the University’s 1898-1899 Annual Report of the Provost to the Board of Trustees, it states that Dr. Shurtleff presented the infant mummy to the museum on Christmas Day, as an “admirably preserved specimen and an interesting pathological subject”.

It seems that this mummy came into the collection unwrapped – he only has small amounts of textile preserved on his body (and there is currently no evidence that the cloth partially covering his body in the image above is related to his remains, but this remains to be determined). While the fact that he is unwrapped is unfortunate, it allows us to see how well preserved his remains are and evidence of how his body was mummified, including evisceration through an incision on the left side of his torso.

The open incision on the left side of his body reveals a mostly empty body cavity, containing small bundles of linen.

A CT scan in 2009 further reveals how this boy’s body was mummified, and also reveals damage not visible from the exterior. For example, it is clear that his brain was removed, likely through the nose (but due to the small side of his nasal bones it is not possible to see evidence of this). The scan also reveals a large hole in the left lower side of his skull, and the piece of missing bone resting inside his skull.

Two CT still images show the child mummy’s skull with a piece of bone resting inside the cranium (left) and the hole created as a result of this loss (right).

Oddly, this damage to his skull is not visible from the exterior, but it may be the result of trauma. His cause of death has still not been determined, but this damage may provide a clue.

The information from the CT scan tells us that this child was less than 2 years of age when he died, based on the fact that his fontanelle (the soft spot) is still open, and also on the development of his teeth.

The open fontanelle on the top of the baby’s head is indicated in these 2 images with blue arrows.

The excellent preservation of his body is not the only remarkable thing about this baby boy. While examining his remains, we noticed traces of a green substance in areas, including on his face and fingers.

Left: A detail of the green substance under the boy’s right eye. Right: An overall view of the boy’s face, highlighting the locations of the green substance in a brighter green color.

This substance resembles copper corrosion, and it may either be corrosion from copper that was once in contact with his body (during burial), or may be traces of a green copper-based pigment. How do we know this green substance is copper-based? We tested it with our portable x-ray fluorescence analyzer, which showed high peaks for copper in these areas.

While we’re still working to interpret some of this information, I can tell you one thing for certain: this baby boy mummy sure is special. And if you visit the lab, you just might catch a glimpse of him.

Our table at the Science Festival Press Preview night, featuring our portable XRF analyzer and a Proscope. At right, Lynn demos the Proscope, magnifying a piece of linen at 50X.

Last night, Lynn Grant, Penn Museum Public Relations Director Pam Kosty, and I went to the Franklin Institute for a Press Preview for the 2013 Philadelphia Science Festival. Our museum is hosting a signature event for the Science Festival this year, entitled: “Long Live Our Treasures: The Science of Conservation and Preservation.” We have partnered with 17 other organizations for this program, which will spotlight the typically “behind the scenes” work of conservation professionals through demonstrations, exhibits and short talks. All of this will be taking place on Wednesday April 24 from 5-8pm at the museum.

At the preview last night, we got a taste (literally) of some of the other programming that will be taking place at the Science Festival, including a chance to try fruit from a cacao pod, thanks to Mars Chocolate Research Fellow Ed Seguine (who tastes chocolate for a living – how envious am I?) and a sample of chocolate bourbon habanero ice cream made with liquid nitrogen (so delicious and creamy!) made by the evening’s host, the Franklin Institute.

A partially opened cacao pod (left) and the liquid nitrogen-prepared ice cream being served (right)

At our event for the Science Festival on April 24, we are looking forward to sharing our work in the Artifact Lab – we will be open till 8pm that evening and visitors will have a chance to use our Proscopes (like the one in the image above) and learn about how we are conserving mummies and other Egyptian materials. This event also, appropriately, coincides with National Preservation Week. We’re excited to be hosting this program and highlighting the field of conservation, and we hope that those of you in the Philly area can join us for this!

As part of her graduate studies, Casey has been working on a rare example of an Egyptian child sarcophagus, and instead of recounting the conversation for everyone, I asked her if she’d be willing to answer a few questions for our blog. Read on to hear more about Casey and this fascinating project.

I am working on this project with Dr. David A. Scott and Prof. Ellen Pearlstein, both of whom are faculty in our program. Marie Svoboda, a conservator of antiquities at the Getty Villa, and Dr. Kara Cooney, an Egyptologist at UCLA are advisors.

A view of the upper half of the sarcophagus

2. Tell us more about this child sarcophagus that you’re working on and why it is so unusual (that’s assuming that it is!!)

The sarcophagus (or coffin) lid is on loan for this project from the San Diego Museum of Man. It was given to the museum in 2001 and it dates to the Ptolemaic period, 305 – 30 BCE although the exact date of this object is not known. It is unusual because sarcophagi were costly and rarely made for children. This is supposed to be one of only seven from this period known to exist. It seems to have been for a girl, and scholars I consulted suggest she may have been a child wife, which would justify the expense. Many people have asked about the mummy and the base of the coffin but these are unknowns.

It is made of a carved out section of a tree trunk with pieces added to create the chest, face and foot. Wood dowels were used to secure the pieces in place. The exterior is completely covered with a polychrome layer made up of a base of a brown granular paste, then a white “gesso” layer and the paint applied onto that. The interior is unpainted.

A side view of the sarcophagus in the UCLA/Getty labs

3. What is your ultimate goal for this project?

The project is a technical analysis of the structure and materials, and development of a treatment plan. The treatment goal is to stabilize the structure and fragile paint layer, and reduce or removal modern fills that may be damaging the original materials. If the museum approves I will carry out treatment in selective areas to establish a protocol so the museum can continue the work after the coffin returns to San Diego in June.

4. Since I get asked this question almost every day, I’m going to turn around and ask you – what is the most interesting and/or unexpected thing that you’ve found so far in your work on the sarcophagus?

It is a fascinating project in so many ways, but two things come to mind. One involves the manufacture, and the other a mysterious surface condition.

The ancient Egyptians frequently reused parts of coffins and I have found evidence of reuse here. X-rays reveal empty dowel holes that indicate changes in the structure, and there are modern metal screws holding the foot block in place.

X-radiographs of the head (left) and foot (right) of the sarcophagus. Note the modern screws holding the foot together.

Scholars I have consulted find the carving of the face more consistent with earlier periods. I am examining the types of wood and indications of changes in the construction, and analyzing the pigments, gesso, fill materials, and coatings to identify differences that might point to different sources for the different parts.

The most unexpected development was the emergence of small waxy exudates on the lower front of the “torso”. I am doing chemical tests on samples, and FTIR (Fourier transform infrared spectroscopy) is being carried out by Getty Conservation Institute Scientist Herant Khanjian to identify the substance and determine whether it poses a threat to the original materials. This is probably the result of a coating or consolidant that was put on the object, but there is no record of its treatment before SDMM acquired it.

Thanks Casey! This is a terrific project, and a great example of how conservation is often a very collaborative process, involving conservators, scientists, archaeologists, and other specialists.

I will be keeping up with Casey as her work progresses. For more information on the UCLA/Getty Conservation Program and other student projects, follow the links I’ve included in the text above.

A couple weeks ago we brought out our portable X-ray fluorescence (pXRF) analyzer to aid in our study of some of the objects in the Artifact Lab. We provided an overview of this session earlier on our blog-read more by clicking here.

One of the objects that we looked at with the pXRF is this painted wooden coffin. I also wrote a blogpost about this artifact and you can read more about it there.

Painted wooden coffin of Tawahibre

A critical part of the conservation process is examining and documenting objects-their materials, technology, and condition-all of this information is recorded in condition/treatment reports. Beyond saying that this coffin was decorated with red, yellow, white, black, and blue paint, we would like to provide more information in our report about which pigments were used, if possible. Based on knowledge of the painting materials used in ancient Egypt, we had some ideas, and we were hoping that the pXRF could confirm that our ideas were on the right track.

One pigment we were interested in knowing about is the blue. Here is a detail of the blue paint in one area:

Detail of coffin, showing blue paint

Considering that Egyptian blue was the principal blue pigment used in ancient Egypt, this was our first guess. Egyptian blue is a synthetic pigment, one of the first synthetic pigments ever produced, made by heating together copper, silica (sand), lime (calcium oxide) and an alkali such as natron (sodium sesquicarbonate). This pigment is found on objects from as early as the 4th Dynasty through to the Roman Period. The hue varies from dark to light blue, depending on the components and the grinding process (or the final particle size). Dark blue colors tends to have a larger particle size and smaller particles produce a lighter blue.

So how can the pXRF help us understand what blue pigment was used on this coffin? Well, as previously described, XRF is useful for identifying elements present in a sample or targeted area of an object. We simply positioned the pXRF in contact with the area of interest, in this case, a stable area of the blue paint, and took a reading.

The pXRF analyzer positioned in contact with the target area of interest

The reading produced a spectrum with peaks representing the x-ray energies of the elements present.

pXRF spectrum of the blue paint from the coffin

Here we have labeled the peaks of each element detected-you can see that there are very high peaks for Calcium and Copper. This is what we would expect to see for an Egyptian blue pigment!

We’re looking forward to continuing to use this technique for examining other objects in the Artifact Lab-especially those artifacts with only traces of paint left or those objects with surfaces that have darkened and where the original colors are more difficult to interpret. We’ll continue to update the blog with this information as we find out more.

One of the boards from the inner coffin of Ahanakht, before treatment.

Previously I began to tell you about this multi-part artifact. Then, I was just starting to get acquainted with it. When conservators first look at any artifact, the first thing we think about is not where it’s from, not how old it is, not even what culture made it. The first and most important fact for conservators is what it’s made of. The material tells us what kind of problems it might have and what kind of treatments we can use or not use – it’s the starting point of everything we do.

The coffin boards are wood, with some paint applied. Four thousand year-old wood. Right away, that tells us something about what kind of wood it must be, since wood generally doesn’t survive so long in the archaeological record. Because there’s been a lot of research done on Egyptian materials, we can say with some confidence that the wood is cedar of Lebanon (Cedrus libani). Cedar is a prized wood because the trees produce chemicals that make them resistant to insect damage and various forms of rot.

A detail of the board showing construction details.

The first step of any treatment is careful examination. The coffin boards, despite being entombed thousands of years ago in the desert environment of Egypt and then brought to Philadelphia with its humid summers and desiccating winter heating seasons, appear to be in excellent condition for the most part; their most obvious problem being a thick coat of dust from uncovered storage for many decades. I documented the appearance of the board, noting its construction details, such as four wooden pegs and mitered edges. One curious feature was thin metal ribbons running in channels along the long axis of the board. I was unsure whether these were an original feature or something done in modern times to put the coffin back together. It seemed an unusually elaborate repair but the metal was in such good condition that I didn’t think it was 4000 years old. Even under a microscope, I couldn’t tell exactly what the metal was. There were slight traces of green corrosion, which usually means copper or copper alloy, but the metal was mostly dark grey and quite flexible, so it could be lead. I made a note to analyze it using our new portable X-ray fluorescence analyzer which has since happened and to do some research on Egyptian coffin technology. Dr. Joe Wegner, also an Associate Curator in the Egyptian Section, recommended a book about a similar coffin at the Boston Museum of Fine Arts (The Secrets of Tomb 10b) and there I found this information: “the sides have beveled edges fastened together by dowels and copper ribbons“. So it looks like those metal ribbons are original. Perhaps their unusually excellent condition has something to do with the cedar around them.

During treatment, showing dirt partially removed and tools used for cleaning.

Treatment was relatively straightforward. I used a HEPA-filtered vacuum with variable speed control to remove the loose dust from the surface of the board. Conservators choose their cleaning methods based on the type of dirt to be removed and the substrate from which it is to be removed. ‘Dry’ cleaning methods (those not using liquids such as water or other solvents) are generally less likely to damage the artifact and are preferred wherever possible, although care must still be taken to ensure that only the dirt is removed and not any of the original surface. By using a very small vacuum attachment at low speed and monitoring the process closely using a magnifying visor, I was able to clean the surface safely. Not very glamorous but I’ve discovered that this artifact has a pretty important role in the history of archaeological science – see my post on the Museum’s blog for information on that!

What can we do with a pXRF, you might ask? Well, Nina Owczarek provides a good overview about the use of this instrument in a previous post and also in a presentation which you can watch by following this link.

I’ve used a pXRF before, but it’s been awhile, so today Nina came up and gave us all a refresher. Essentially, x-ray fluorescence is a non-destructive analytical method that uses x-rays to identify elements present in objects or samples. This technique is particularly useful for characterizing pigments and metal alloy components, and that is what we’re using it for in the Artifact Lab.

A view of Nina and I discussing the pXRF from outside the lab

After examining a few artifacts visually, we had some questions about materials and wanted to do some further investigation with the pXRF. For instance, we are interested in these metal ribbons on the Ahanakht coffin boards (see Lynn Grant’s previous post about the boards).

The pXRF positioned in contact with the metal ribbons on one of the smaller coffin boards

After examination of these ribbons under the microscope, it was still difficult to determine what type of metal they are made of. With the pXRF, after a 180-second scan and using special software, a spectrum was produced that showed a large peak for copper and very small peaks for tin, iron, arsenic and lead. We haven’t been able to analyze the data much yet, but this does tell us that these are indeed made of copper.

We will follow this post soon with more information and interpretation of our results.